1. Field of the Invention
The invention is based on a damper, and in particular used in a shock absorber for a vehicle.
2. Description of the Prior Art
In conventional passive shock absorber pistons, spring packets, comprising a plurality of spring disks, are as a rule used for generating a certain characteristic curve for the damping force. In the conventional shock absorber piston, the spring rate of the spring packet is determined once and for all during development and after that can no longer be adjusted. This principle makes an economical, robust construction of a damper piston possible, with at the same very good, time-tested courses of the characteristic damper curves.
In the prior art, dampers for vehicles are also known with adjustable damper pistons, which as a rule operate on the principle of a variable opening cross section. These dampers adjust the appropriate characteristic shock absorber values via hydraulic proportional valves and can be adapted to various driving situations. The proportional valves, for instance with the aid of a control piston that is moved by an exciter coil, control the fluid flow in the damper continuously. The proportional valves are either flanged to the damper or integrated with the piston plunger of the damper. An additional sensor, which is disposed on the wheel suspension, furnishes information about the running-in state of the damper. As the sensors, acceleration sensors or travel sensors can be used. Associated evaluation and control units are either disposed centrally in the vehicle or can be disposed noncentrally on the flanged-on proportional valve. The proportional valve may for instance indirectly control the main fluid flow; that is, a small secondary flow is regulated directly by a small control piston and forms a pressure difference with the main valve. The main fluid flow in the main valve is adjusted on the basis of this regulated pressure difference. As a result, it is attained that with relatively low adjusting forces, a relatively high pressure can be controlled. The reaction time of the damper is limited by the transient response of the proportional valve.
In German Patent Application DE 10 2006 037 172.0, not published prior to the priority date of the present application, of the present applicant, a damper with a damper cylinder is described, in which a piston plunger is guided via a piston rod, and for adjusting characteristic damper values the flow of a damper fluid is regulated. Regulators, which have two independent closed-loop control circuits for a tension stage and a compression stage, are disposed inside the damper cylinder, and during the compression stage period, the regulators regulate the flow of the damper fluid in a first flow direction by a first adjusting element and during the tension stage period they regulate the flow of the damper fluid in a second flow direction by a second adjusting element. One possible adjustment variable of the first adjusting element for an ensuing compression stage period is adjustable by associated first predetermining element during the tension stage period chronologically preceding this compression stage period, and one possible adjustment variable of the second adjusting element for the ensuing tension stage period is adjustable by associated second predetermining element during the compression stage period chronologically preceding that tension stage period.